1. Field of the Invention
The present invention relates to a pulverizing and classifying apparatus for solids, including but not limited to, minerals, chemicals, and medical substances, such as talcs, limes, ceramics, resins, cosmetics, dyes, and Chinese medicines, and more particularly to a pulverizing and classifying apparatus for a toner.
2. Discussion of the Background
A typical fluidized bed (jet) pulverizer is formed of a pulverizing chamber, a collision member, and a nozzle, wherein the nozzle sprays a rapid gas to pulverize coarse particles. Various suggestions have been made to improve such a fluidized bed pulverizer.
For example, Japanese Laid-Open Patent Publication No. 2000-107626 discloses a method of using multiple tiered nozzles to improve the pulverizability, wherein, for an observer looking into the pulverizer from above, the nozzles do not overlap each other. Japanese Laid-Open Patent Publication No. 2000-15126 discloses a method of positioning a cylindrical board to separate a flow passage leading to a classifier from another leading to a pulverizer. Japanese Laid-Open Patent Publication No. 2000-5621 discloses a method of locating a pyramid-type projection having sloped sides in the shape of isosceles triangles placed at the bottom center of a pulverizing chamber, facing each nozzle, wherein a range is specified for the angle between an axis of a collision member located in a vertical section that includes the nozzle axis and a central axis of the pulverizing chamber.
Conventional pulverizing and classifying methods will now be explained, referring to the fluidized bed apparatus shown in FIG. 1. The fluidized bed pulverizing and classifying apparatus 1 is capable of pulverizing a heated material by spraying compressed air from a pulverizing nozzle 6, causing the temperature of the fluidized bed apparatus to decrease due to the adiabatic expansion of the air, thereby making the fluidized bed apparatus suitable for surface pulverization because of the variation in relative velocity of the accelerating solid material being pulverized induced by the compressed air sprayed into the apparatus.
The material to be pulverized enters a classifying rotor 2 as a coarse powder and is classified as a conforming material. However, the contact between the solid materials being pulverized tend to generate a fine powder.
The above-mentioned conventional technologies are insufficient to improve pulverizability. In order to prevent a coarse powder from slipping into conforming materials and to control the amount of fine powder generated due to excessive pulverization, the present inventors disclose a fluidized bed pulverizing and classifying apparatus in Japanese Laid-Open Patent Publication No. 2002-276526, wherein a pulverizing position adjustor capable of adjusting a distance between the bottom of the pulverizer and the pulverizing nozzle is installed to control the amount of material to be pulverized introduced around the pulverizing nozzle in order to decrease the gas-particle ratio at a classifying rotor such that only the material to be pulverized constantly cover a circumference of the rotor.
Excessive pulverization is prevented by controlling a pulverization pressure in order to reduce particle collision speeds. However, fluidization of the materials to be pulverized deteriorates when the collision speed is reduced, preventing the materials to efficiently reach the classifying rotor and thereby resulting in excessive pulverization due to a deterioration of the particle classification process.
Based at least on the foregoing reasons, a need exists for a new fluidized bed pulverizing and classifying apparatus that has a simple constitution and a high capacity while maintaining a high degree of flexibility.